Partial pressure swing adsorption system for providing hydrogen to a vehicle fuel cell

ABSTRACT

A method of operating a fuel cell system includes providing a fuel inlet stream into a fuel cell stack, operating the fuel cell stack to generate electricity and a hydrogen containing fuel exhaust stream, separating at least a portion of hydrogen contained in the fuel exhaust stream using partial pressure swing adsorption, and providing the hydrogen separated from the fuel exhaust stream to a hydrogen storage vessel or to a hydrogen using device.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of fuel cellsystems and more particularly to fuel cell systems with anode exhaustfuel recovery by partial pressure swing adsorption.

SUMMARY OF THE INVENTION

Fuel cells are electrochemical devices which can convert energy storedin fuels to electrical energy with high efficiencies. High temperaturefuel cells include solid oxide and molten carbonate fuel cells. Thesefuel cells may operate using hydrogen and/or hydrocarbon fuels. Thereare classes of fuel cells, such as the solid oxide regenerative fuelcells, that also allow reversed operation, such that oxidized fuel canbe reduced back to unoxidized fuel using electrical energy as an input.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2A, 2B, 2C, 2D, 3, and 4 are schematic diagrams of the partialpressure swing adsorption systems of the embodiments of the invention.

FIGS. 5 and 6 are schematic diagrams of fuel cell systems of theembodiments of the invention which incorporate the partial pressureswing adsorption systems.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the invention provide a system and method in whichpartial pressure swing adsorption (i.e., concentration swing adsorption)is used to separate hydrogen from a high temperature fuel cell stackfuel exhaust stream and to provide the separated hydrogen as fuel to ahydrogen storage vessel or to a hydrogen using device, such as a lowtemperature fuel cell stack used to power a vehicle. If desired, atleast a portion of the separated hydrogen may also be recycled into thefuel inlet stream of the high temperature fuel cell stack. Preferably,the high temperature fuel cell stack comprises a solid oxide fuel cellstack which operates on hydrocarbon fuel and the low temperature fuelcell stack comprises a PEM fuel cell stack which operates on hydrogenfuel. The first four embodiments described below are directed to variouspartial pressure swing adsorption gas separation methods and deviceswhich may be used to separate hydrogen from the fuel exhaust stream,while the fifth and sixth embodiments are directed to the fuel cellsystems which use partial pressure swing adsorption methods and devicesfor hydrogen separation.

The first embodiment of the invention provides a four-step partialpressure swing adsorption (i.e., concentration swing adsorption) cyclefor gas separation, such as for recovering fuel from the fuel (i.e.,anode side) exhaust of a solid oxide fuel cell stack. Two beds packedwith an adsorbent material, such as activated carbon, are used to adsorbcarbon dioxide and water (i.e., water vapor) from the fuel exhaust,allowing hydrogen and carbon monoxide to pass through the beds. The bedsare regenerated, preferably countercurrently, with air dried to modestrelative humidities, such as about 30% to about 50% relative humidity.For example, dry air for regeneration may be developed in a temperatureswing adsorption cycle using silica gel or activated alumina. Flushsteps are used to recover additional hydrogen and to prevent air fromcontaminating the recovered fuel. The duration of the adsorption andregeneration (i.e., feeding and purging) steps is preferably at least 5times longer, such as 10-50 times longer than the duration of the flushsteps.

Thus, a reliable, energy-efficient cycle for optimum gas separation isprovided. For example, the cycle is a high efficiency cycle for maximumrecovery of hydrogen and maximum rejection of carbon dioxide and air,based on a partial pressure swing adsorption (also referred to herein asconcentration swing adsorption) with countercurrent purge and cocurrentflush steps. Since the beds are preferably regenerated with air, thesweeping of air left in the bed at the end of regeneration back into thefuel cell stack is not desirable. Furthermore, at the start of aregeneration step, the bed taken off stream contains hydrogen in the gasphase. Recovery of this hydrogen is desirable. The flush steps are usedto remove the air left in the bed at the end of regeneration to preventproviding this air back into the fuel cell stack, and to provide thehydrogen remaining in the bed at the start of a regeneration step intothe fuel inlet of the fuel cell stack.

While the system and method of the first embodiment will be describedand illustrated with respect to an adsorption system which separatescarbon dioxide from the hydrogen in a solid oxide fuel stack fuelexhaust stream, it should be noted that the system and method of thefirst embodiment may be used to separate any multicomponent gas streamthat is not part of a fuel cell system or that is part of a fuel cellsystem other than a solid oxide fuel cell system, such as a moltencarbonate fuel cell system for example. Thus, the system and method ofthe first embodiment should not be considered limited to separation ofhydrogen from carbon dioxide. The adsorbent material in the adsorbentbeds may be selected based on the gases being separated.

FIG. 1 illustrates a gas separation apparatus 1 of the first embodiment.The apparatus 1 contains a first feed gas inlet conduit 3, which inoperation provides a feed gas inlet stream. If the apparatus 1 is usedto separate hydrogen from a fuel cell stack fuel exhaust stream, thenconduit 3 is operatively connected to the fuel cell stack anode exhaust.As used herein, when two elements are “operatively connected,” thismeans that the elements are directly or indirectly connected to allowdirect or indirect fluid flow from one element to the other. Theapparatus 1 also contains a second purge gas inlet conduit 5, which inoperation provides a purge gas inlet stream.

The apparatus contains a third feed gas collection conduit 7, which inoperation collects at least one separated component of the feed gas. Ifthe apparatus 1 is used to separate hydrogen from a fuel cell stack fuelexhaust stream and to recycle the hydrogen into the fuel inlet of thefuel cell stack, then conduit 7 is operatively connected to the fuelinlet of the fuel cell stack (i.e., either directly into the stack fuelinlet or to a fuel inlet conduit which is operatively connected to thestack fuel inlet). The apparatus also contains a fourth purge gascollection conduit 9, which in operation collects the feed gas outletstream during the flush steps and collects the purge gas outlet streamduring feed/purge steps.

Thus, if the apparatus 1 is used to separate hydrogen from a fuel cellstack fuel exhaust stream, then the first conduit 3 comprises ahydrogen, carbon dioxide, carbon monoxide and water vapor inlet conduit,the second conduit 5 comprises a dry air inlet conduit, the thirdconduit 7 comprises a hydrogen and carbon monoxide removal and recyclingconduit and the fourth conduit 9 comprises a carbon dioxide and watervapor removal conduit.

The apparatus 1 also contains at least two adsorbent beds 11, 13. Thebeds may contain any suitable adsorbent material which adsorbs at leasta majority, such as at least 80 to 95% of one or more desired componentsof the feed gas, and which allows a majority of one or more othercomponents to pass through. For example, the bed material may comprisezeolite, activated carbon, silica gel or activated alumina adsorbentmaterial. Activated carbon is preferred for separating hydrogen andcarbon monoxide from water vapor and carbon dioxide in a fuel cell stackfuel exhaust stream. Zeolites adsorb carbon dioxide as well. However,they adsorb water very strongly, and a very dry gas should be used forregeneration, which is difficult to obtain. Thus, zeolite beds canpreferably, but not necessarily, be used to separate a gas stream whichdoes not contain water vapor because an apparatus which uses zeolitebeds to separate a water vapor containing gas may experience a slowdegradation of performance.

The apparatus 1 also comprises a plurality of valves which direct thegas flow. For example, the apparatus may contain three four-way valveswith “double-LL” flow paths: a feed valve 15, a regeneration valve 17and a product valve 19. The feed valve 15 is connected to the firstconduit 3, to the two beds 11, 13 and to the regeneration valve 17 byconduit 21. The regeneration valve 17 is connected to the second andfourth conduits 5 and 9, respectively, to the feed valve 15 by conduit21 and to the product valve 19 by conduit 23. The product valve 19 isconnected to the third conduit 7, to the two beds 11, 13 and to theregeneration valve 17 by conduit 23. The four-way valves may be used toredirect two flows at a time. Such valves are available in a wide rangeof sizes, for example, from A-T Controls, Inc., Cincinnati, Ohio, USA.If desired, each 4-way valve may be replaced by two 3-way valves or four2-way valves, or by an entirely different flow distribution systeminvolving a manifold.

Thus, the valves 15, 17, 19 are preferably operated such that the purgegas inlet stream is provided into the beds 11, 13 countercurrently withthe feed gas inlet stream during the purge steps and cocurrently withthe feed gas inlet stream during the flush steps. In other words, thefirst conduit 3 is operatively connected to the first and the secondbeds 11, 13 to provide the feed gas inlet stream into the first and thesecond beds in a first direction. The second conduit 5 is operativelyconnected to the first and the second beds 11, 13 through valves 17, 19such that the purge gas inlet stream is provided into each of the firstand the second beds 11, 13 in a different direction from the firstdirection (such as in the opposite direction) during the first and thesecond feed/purge steps, and the purge gas inlet stream is provided intothe first and the second beds in the first direction (i.e., the samedirection and the feed gas inlet stream) during the first and the secondflush steps.

FIGS. 2A-2D illustrate the steps in the operation cycle of system 1.FIG. 2A shows the apparatus 1 during a first feed/purge step in whichthe first bed 11 is fed with a feed gas inlet stream, such as the fuelstack fuel exhaust stream, while the second bed 13 is fed with a purgegas, such as dried air, to regenerate the second bed 13.

The feed gas inlet stream is provided from conduit 3 through valve 15into the first adsorbent bed 11. For a feed gas which contains hydrogen,carbon monoxide, carbon dioxide and water vapor, the majority of thehydrogen and carbon monoxide, such as at least 80-95% passes through thefirst bed 11, while a majority of the carbon dioxide, such as at least80-95%, and much of the water vapor are adsorbed in the first bed. Thefeed gas outlet stream comprising at least one separated component ofthe feed gas, such as hydrogen and carbon monoxide, passes through valve19 and is collected at a first output, such as the third conduit 7.

The purge gas inlet stream, such as dried air, is provided from thesecond conduit 5 through valve 17, conduit 23 and valve 19 into a secondadsorbent bed 13. The purge gas outlet stream passes through conduit 21and valves 15 and 17, and is collected at a second output, such as thefourth conduit 9.

In the first feed/purge step, the valve positions are such that valve 15directs the feed to the first bed 11 and valve 19 directs the hydrogenproduct away to conduit 7. Valve 17 is positioned to sweep dry aircounter currently through the second bed to remove carbon dioxide thatwas previously adsorbed. Some of the water in the feed gas steam isadsorbed on the adsorbent material, such as activated carbon, at theinlet of the first bed 11 and will be removed from the bed 11 when it isregenerated in a subsequent step. Carbon monoxide will be passed throughthe first bed 11 as the carbon dioxide wave advances.

FIG. 2B illustrates the apparatus 1 in a first flush step which isconducted after the first feed/purge step. In this step, the feed valve15 and the regeneration valve 17 switch flow directions from the priorstep, while the product valve 19 does not.

The purge gas inlet stream is provided from conduit 5 through valves 17and 15 and conduit 21 into the first adsorbent bed 11. Preferably, thispurge gas inlet stream is provided into the first bed 11 in the samedirection as the feed gas stream in the previous step. The purge gasoutlet stream, which comprises at least one component of the feed gas,such as hydrogen, that was trapped in a void volume of the firstadsorbent bed, is collected at the first output, such as conduit 7.

The feed gas inlet stream is provided from conduit 3 through valve 15into the second adsorbent bed 13. The feed gas outlet stream, whichcomprises a portion of the purge gas, such as air, that was trapped in avoid volume of the second bed 13, passes through valves 19 and 17 andconduit 23 and is collected at an output different from the firstoutput, such as at conduit 9.

Thus, in the first flush step, hydrogen trapped in the void volume ofthe first bed 11 is swept to product by the entering air and desorbingcarbon dioxide. Air trapped in the void volume of the second bed 13 ispurged from the bed 13 by the entering feed gas. This step improves theoverall efficiency of the process by continuing to recover hydrogen thatis trapped from the prior feed step and preventing air from the priorpurge step from contaminating the hydrogen containing product after thenext valve switch. This flush step is short, such as less than ⅕ of thetime of the prior feed/purge step, such as 1/10 to 1/50 of the time ofthe prior step. For example, for an about 90 second feed/purge step, theflush step may be about 4 seconds.

FIG. 2C shows the apparatus 1 during a second feed/purge step which isconducted after the first flush step. In this step, the second bed 13 isfed with a feed gas stream, such as the fuel stack fuel exhaust stream,while the first bed 11 is fed with a purge gas, such as dried air, toregenerate the first bed 11. Thus, in this step, the flow paths invalves 17 and 19 switch. This step is generally the same as the firstfeed/purge step, but with the beds reversed.

The feed gas inlet stream is provided from conduit 3 through valve 15into the second adsorbent bed 13. Preferably the feed gas inlet streamis provided into the second bed 13 in the opposite (i.e.,countercurrent) direction from the direction in which the purge gasinlet stream is provided into the second bed 13 in the first purge step.The feed gas outlet stream, which comprises at least one separatedcomponent of the feed gas, such as hydrogen and carbon monoxide, iscollected at the first output, such as in the third conduit 7. The purgegas inlet stream is provided from conduit 5 through valves 17 and 19 andconduit 23 into the first adsorbent bed 11. Preferably the purge gasinlet stream is provided into the first bed 11 in the opposite (i.e.,countercurrent) direction from the direction in which the feed gas inletstream is provided into the first bed 11 in the first feed step. Thepurge gas outlet stream is collected from the first bed 11 at an outputdifferent from the first output, such as at the fourth conduit 9.

FIG. 2D illustrates the apparatus 1 in a second flush step which isconducted after the second feed/purge step. In this step, the feed valve15 and the regeneration valve 17 switch flow directions from the priorstep, while the product valve 19 does not. This step is similar to thefirst flush steps, but with the beds reversed.

The purge gas inlet stream is provided from conduit 5 through valves 17and 15 and conduit 21 into the second adsorbent bed 13. Preferably, thissteam is provided into the bed 13 in the same direction as the feed gasinlet stream in the prior two steps. The purge gas outlet stream, whichcomprises at least one component of the feed gas, such as hydrogen, thatwas trapped in a void volume of the second adsorbent bed 13, iscollected at the first output, such as the third conduit 7.

The feed gas inlet stream is provided from conduit 3 through valve 15into the first adsorbent bed 11. The feed gas outlet stream, whichcomprises a portion of the purge gas, such as air, that was trapped in avoid volume of the first bed 11, is collected at an output differentfrom the first output, such as at the fourth conduit 9. Then the firstfeed/purge step shown in FIG. 2A is repeated. In general, the four stepsdescribed above are repeated a plurality of times in the same order.

It should be noted the feed gas inlet stream is preferably provided ineach of the first 11 and the second 13 adsorbent beds in the samedirection in the steps described above. In the first and the secondflush steps, the purge gas inlet stream is provided into each of thefirst and the second adsorbent beds in the same direction as the feedgas inlet stream direction. In contrast, in the first and the secondfeed/purge steps, the purge gas inlet stream is provided into each ofthe first and the second adsorbent beds in a different direction, suchas the opposite direction, from the feed gas inlet stream direction.

The countercurrent purge gas inlet stream flow is advantageous becauseit is believed that it will reduce the amount of carbon dioxide in thehydrogen product stream compared to a co-current flow during the purgesteps. Some water will adsorb near the inlet of the carbon bed duringthe feed step. During the purge or regeneration step, the bed is purgedcounter currently with dried air. Because activated carbon is used foradsorption of carbon dioxide and activated carbon does not adsorb waterappreciably at moderately low relative humidities, in order to preventaccumulation of water in the bed, the regeneration purge only needs tobe dried to a relative humidity of roughly 30 to 50%. During the feedstep, carbon monoxide will be pushed into the product (with thehydrogen) by using the beds efficiently for carbon dioxide removal(i.e., by advancing the carbon dioxide wave reasonably far into thebeds). The countercurrent regeneration step will reduce the level ofcarbon dioxide in the hydrogen stream in comparison to a cocurrentregeneration step. The dual flush step will maximize both hydrogenrecovery and air rejection from the hydrogen product.

As noted above, in the partial pressure swing adsorption method, thefeed gas inlet stream is not pressurized prior to being provided intothe first and the second adsorbent beds. Furthermore, the above foursteps are preferably conducted without external heating of the adsorbentbeds.

In operation, the first bed 11 performs the following functions. Itreceives the feed gas inlet stream from the first conduit 3 and providesat least one separated component of the feed gas to the third conduit 7in a first feed/purge step. It receives the purge gas inlet stream fromthe second conduit 5 and provides a purge gas outlet stream, whichcomprises at least one component of the feed gas that was trapped in avoid volume of the first bed to the third conduit 7 in a first flushstep. It receives a purge gas inlet stream from the second conduit 5 andprovides a purge gas outlet stream to an output different from the thirdconduit 7, such as the fourth conduit 9, in a second feed/purge step. Italso receives the feed gas inlet stream from the first conduit 3 andprovides a feed gas outlet stream, which comprises a portion of thepurge gas that was trapped in a void volume of the first bed, to at anoutput different from the third conduit 7, such as the fourth conduit 9,in a second flush step.

In operation, the second bed 13 performs the following functions. Itreceives a purge gas inlet stream from the second conduit 5 and providesa purge gas outlet stream to at an output different from the thirdconduit 7, such as the fourth conduit 9, in a first feed/purge step. Itreceives the feed gas inlet stream from the first conduit 3 and providesthe feed gas outlet stream, which comprises a portion of the purge gasthat was trapped in a void volume of the second bed 13, to an outputdifferent from the third conduit 7, such as the fourth conduit 9, in afirst flush step. It receives the feed gas inlet stream from the firstconduit 3 and provides the feed gas outlet stream comprising at leastone separated component of the feed gas to the third conduit 7 in asecond feed/purge step. It also receives the purge gas inlet stream fromthe second conduit 5 and provides the purge gas outlet stream, whichcomprises at least one component of the feed gas that was trapped in avoid volume of the second bed 13 to the third conduit 7 in a secondflush step.

Thus, at least a majority of the carbon dioxide and water vapor in thefeed gas inlet stream is adsorbed by the first 11 and the second 13adsorbent beds during the first and the second feed/purge steps,respectively. The adsorbed carbon dioxide and water vapor is removedfrom the first and the second adsorbent beds by the purge gas inletstream during the second and the first feed/purge steps, respectively.The removed carbon dioxide and water vapor are collected with the purgegas outlet stream at the second output during the second and the firstfeed/purge steps.

It is noted that the regeneration (i.e., purging) of the bed will beaccompanied by a cooling of the bed as CO₂ desorbs. It is believed thatthis will shift adsorption equilibrium to lower partial pressures forCO₂ and will slow regeneration. This and the expanding velocity frontduring regeneration may be taken into account in setting the purge gas(i.e., dry air) flow rate. For example, the inlet air volumetricflowrate for regeneration may be greater than, such as 1.5 times greaterthan, the outlet flowrate of hydrogen and carbon monoxide. It isbelieved that allowing for desorption of carbon dioxide duringregeneration, the outlet flowrate for regeneration will exceed the inletflowrate of the feed.

The apparatus 1 may have the following non-limiting features. Theadsorbent bed material preferably comprises activated carbon forhydrogen separation from the fuel cell stack fuel exhaust. For example,Calgon BPL activated carbon, 6×16 or 4×10 mesh may be used. The beds 11,13 may be cylindrical beds 2-12 inches in diameter and 1-6 feed long,such as 6 inches in diameter and 3 feet long, for example, depending onthe size of the fuel cell stack and on the flow rate of the gases. Theduration of the feed/purge steps may be more than 1 minute while theduration of the flush steps may be a few seconds. For example, thefeed/purge duration may be 1 to 3 minutes, such as 1.5 minutes, whilethe flush duration may be 3-5 seconds, such as 4 seconds.

The method of the first embodiment is designed to provide a highhydrogen recovery (with flush steps), high carbon dioxide separation(with flush and countercurrent regeneration steps), high degree of airrejection (with flush steps), regeneration using a purge gas having arelatively low dryness, such as air having 30-50% relative humidity, lowenergy requirements, high robustness (i.e., easily tunable and adaptableto changes in operating conditions), simple operation with few movingparts, high scalability, and low to moderate capital cost.

The dry air for the purge steps may be obtained by any suitable method.For example, the dry air can easily be achieved using temperature swingadsorption cycle with water vapor absorbing beds, such as silica gel oractivated alumina beds. Silica gel has a somewhat higher capacity forwater than alumina. However, it will fracture if very dry and contactedwith a water mist. If this is likely, a protective layer of anon-decrepitating silica gel can be used, or activated alumina can beused.

The temperature swing adsorption cycle uses two beds (i.e., beds otherthan beds 11, 13 shown in FIG. 1). One bed is used in the adsorptionmode while the other is being regenerated (heated and cooled). The stepsin the cycle are as follows.

In a first adsorption step, a working capacity of 10 mol H₂O/kg ofsilica gel can be used. Considering the worst case, the air would besaturated with water at 30° C. The partial pressure of water in airsaturated at 30° C. is 0.042 bar. For example, to produce a dry air flowrate of 144 slpm from this wet air, 0.28 mol/min of water must beremoved. At the designated working capacity, silica gel is consumed at arate of 0.028 kg/min. A bed containing 2 kg of silica gel can remain onstream for 72 minutes. Given a specific gravity of silica gel of 0.72(corresponding to a bulk density of 45 lb/ft³), the bed will dry 4300bed volumes of feed during this time (with 12,000 temperature correctedliters of wet feed dried by a bed 2.8 liters in volume). The dried airis provided through conduit 5 into the apparatus 1.

In a second heating step, the bed is heated counter currently with awarm feed (e.g., 80° C. or other suitable moderately warm or hottemperature). The bed is heated after about 1000 bed volumes have beenpassed into it. Somewhat more energy will be required to heat metalparts also.

In a third cooling step, the bed is cooled cocurrently (same directionas adsorption) with the wet air feed. It will take about 800 bed volumesto cool the bed. This will deposit water at the bed inlet and use upsome of the capacity for adsorption, reducing it to about 3500 bedvolumes. While the first bed is undergoing the adsorption step, thesecond bed is undergoing heating or cooling steps. While the second bedis undergoing the adsorption step, the first bed is undergoing heatingor cooling steps.

It should be understood that the calculation above is highlyconservative and approximate. It is based on air for regeneration thatis available saturated with water at 30° C. Typically, the air will bedrier. The regeneration requirements for the carbon beds are mild (e.g.,30-50% RH). Indeed, on a cool day or a dry day, drying the regenerationair would not be necessary. Also, if the driers went out of service fora short time, the process would not be endangered.

In a second embodiment of the invention, the apparatus 31 operates witha countercurrent purge but with no flush steps. FIG. 3 shows apparatus31 using a simple cycle with a countercurrent purge but no flush. Twoinstead of three four-way valves 15, 17 are used. The apparatus 31 andmethod of using this apparatus are otherwise similar to the apparatus 1and method of the first embodiment, except that the first and secondflush steps are omitted.

The advantage of countercurrent purge is that carbon dioxide is removedfrom the bed outlet for the feed step, and higher hydrogen purities willresult. But without the flush, about 5% of the hydrogen is notrecovered, and air will somewhat contaminate the hydrogen containingproduct in conduit 7.

In a third embodiment of the invention, the apparatus 41 operates with acocurrent purge with the flush steps. FIG. 4 shows the apparatus 41using a cocurrent purge and flush. It also uses two instead of threefour-way valves. The apparatus 41 and method of the third embodiment inmany respects resembles the apparatus 1 and method of the firstembodiment, except that the purge gas inlet stream is provided into thebeds in the purge steps in the same direction as the feed gas inletstream in the prior feed steps. The negative aspect of this cocurrentcycle is that any CO₂ left in the bed will be most concentrated near theoutlet end for the adsorption step and will somewhat contaminate thehydrogen containing product provided to conduit 7.

In a fourth embodiment of the invention, the air purge gas is notpre-dried. In this embodiment, the apparatus may contain two or threecarbon dioxide adsorbing beds. Some three-bed cycles that do not needdried air. For example, a bed of carbon used for carbon dioxideadsorption will slowly accumulate water from both the fuel cell stackfuel exhaust and the wet regeneration air. The bed could be used formany cycles, with decreasing capacity before it is completelyregenerated. If regenerated counter currently, it would last longer thanif regenerated cocurrently because water deposited during feed stepswould be partially removed by the regenerating air and vice versa.Nevertheless, the bed would accumulate water over time.

In this embodiment, three beds would be used, with two actively runningadsorption and regeneration cycles, as in the first embodiment, while athird bed is being more thoroughly regenerated by a thermal swingregeneration or by purging with a dried gas.

Furthermore, if atmospheric air were reasonably dry (i.e., RH<50% at 30°C.), then the partial pressure adsorption cycle may be used with twobeds in exactly the same configuration as in the first embodiment. Thepurge gas would not deposit a significant amount of water on the carbon,and the countercurrent sweep of the air during regeneration would removewater adsorbed from the fuel cell stack fuel exhaust feed. Thus, if dryair was available from the atmosphere, then a separate air drying stepis not needed.

The fifth and sixth embodiments of the invention illustrate how theadsorption apparatus of the first through fourth embodiments is usedtogether with a fuel cell system, such as a solid oxide fuel cellsystem. It should be noted that other fuel cell systems may also beused.

In the system of the fifth embodiment, a fuel humidifier is used tohumidify the fuel inlet stream provided into the fuel cell stack. In thesystem of the sixth embodiment, the fuel humidifier may be omitted. Aportion of the fuel cell stack fuel exhaust stream is directly recycledinto the fuel inlet stream to humidify the fuel inlet steam. Anotherportion of the fuel cell stack fuel exhaust stream is provided into theadsorption apparatus of any of the first four embodiments, and theseparated hydrogen is then provided to a hydrogen storage vessel or to ahydrogen using device.

FIG. 5 illustrates a fuel cell system 100 of the fifth embodiment. Thesystem 100 contains a fuel cell stack 101, such as a solid oxide fuelcell stack (illustrated schematically to show one solid oxide fuel cellof the stack containing a ceramic electrolyte, such as yttria stabilizedzirconia (YSZ), an anode electrode, such as a nickel-YSZ cermet, and acathode electrode, such as lanthanum strontium manganite).

The system also contains a partial pressure swing adsorption (“PPSA”)unit 1 of any of the first four embodiments comprising a plurality ofadsorbent beds (not shown for clarity). The PPSA unit 1 acts as aregenerative dryer and carbon dioxide scrubber.

The system 100 also contains the first conduit 3 which operativelyconnects a fuel exhaust outlet 103 of the fuel cell stack 101 to a firstinlet 2 of the partial pressure swing adsorption unit 1. For example,the first inlet 2 may comprise the feed valve 15 and/or an inlet to oneof the beds 11, 13, shown in FIG. 1. The system 100 also contains thesecond conduit 5 which operatively connects a purge gas source, such asa dried or atmospheric air source 6 to a second inlet 4 of the partialpressure swing adsorption unit 1. The purge gas source 6 may comprise anair blower or compressor and optionally a plurality of temperature swingcycle adsorption beds.

The system also contains a third conduit 7 which operatively connects anoutlet 8 of the partial pressure swing adsorption unit 1 to the hydrogenstorage vessel or to the hydrogen using device. If desired, the thirdconduit 7 also operatively connects an outlet 8 of the partial pressureswing adsorption unit 1 to a fuel inlet 105 of the fuel cell stack 101,as will be described in more detail below. Preferably, the system 100lacks a compressor which in operation compresses the fuel cell stackfuel exhaust stream to be provided into the partial pressure swingadsorption unit 1.

The system 100 also contains the fourth conduit 9 which removes theexhaust from the unit 1. The conduit 9 may be connected to a catalyticburner 107 or to an atmospheric vent. Optionally, the burner 107 mayalso be operatively connected to the stack fuel exhaust outlet 103 toprovide a portion of the fuel exhaust stream into the burner 107 tosustain the reaction in the burner.

The system 100 also contains a selector valve 108, such as a multi-wayvalve, for example a three-way valve. The selector valve 108 has aninlet operatively connected to an outlet of the partial pressure swingadsorption unit 1, a first outlet operatively connected to the hydrogenstorage vessel or to the hydrogen using device, and a second outletoperatively connected to a fuel inlet 105 of the fuel cell stack 101. Inoperation, the valve 108 divides the hydrogen containing stream providedfrom the PPSA unit 1 into a first stream, which is provided into thehydrocarbon fuel inlet stream, and a second stream which is provided tothe hydrogen storage vessel or to the hydrogen using device.

Preferably, the second outlet of the selector valve 108 is operativelyconnected to the fuel inlet conduit 111 of the fuel cell stack 101 via ablower or a heat driven compressor 109. The device 109 has an inletwhich is operatively connected to the partial pressure swing adsorptionunit 1 (via the selector valve 108) and an outlet which is operativelyconnected to a fuel inlet 105 of the fuel cell stack 101. For example,conduit 7 connects the blower or compressor 109 to the unit 1 via theselector valve 108. In operation, the blower or compressor 109controllably provides a desired amount of hydrogen and carbon monoxideseparated from a fuel cell stack fuel exhaust stream into the fuel cellstack fuel inlet stream. Preferably, the device 109 provides thehydrogen and carbon monoxide into a fuel inlet conduit 111 which isoperatively connected to the a fuel inlet 105 of the fuel cell stack101. Alternatively, the device 109 provides the hydrogen and carbonmonoxide directly into the fuel inlet 105 of the fuel cell stack 101.

The system 100 also contains a condenser 113 and water separator 115having an inlet which is operatively connected to a fuel cell stack fuelexhaust 103 and an outlet which is operatively connected to an inlet 2of the partial pressure swing adsorption unit 1. The condenser 113 andwater separator 115 may comprise a single device which condenses andseparates water from the fuel exhaust stream or they may compriseseparate devices. For example, the condenser 113 may comprise a heatexchanger where the fuel exhaust stream is cooled by a cool counter orco-flow air stream to condense the water. The air stream may comprisethe air inlet stream into the fuel cell stack 101 or it may comprise aseparate cooling air stream. The separator 115 may comprise a water tankwhich collects the separated water. It may have a water drain 117 usedto remove and/or reuse the collected water.

The system 100 further contains a fuel humidifier 119 having a firstinlet operatively connected to a hydrocarbon fuel source, such as thehydrocarbon fuel inlet conduit 111, a second inlet operatively connectedto the fuel cell stack fuel exhaust 103, a first outlet operativelyconnected to the fuel cell stack fuel inlet 105, and a second outletoperatively connected to the condenser 113 and water separator 115. Inoperation, the fuel humidifier 119 humidifies a hydrocarbon fuel inletstream from conduit 111 containing the recycled hydrogen and carbonmonoxide using water vapor contained in a fuel cell stack fuel exhauststream. The fuel humidifier may comprise a polymeric membranehumidifier, such as a Nafion® membrane humidifier, an enthalpy wheel ora plurality of water adsorbent beds, as described for example in U.S.Pat. No. 6,106,964 and in U.S. application Ser. No. 10/368,425, bothincorporated herein by reference in their entirety. For example, onesuitable type of humidifier comprises a water vapor and enthalpytransfer Nafion® based, water permeable membrane available from PermaPure LLC. The humidifier passively transfers water vapor and enthalpyfrom the fuel exhaust stream into the fuel inlet stream to provide a 2to 2.5 steam to carbon ratio in the fuel inlet stream. The fuel inletstream temperature may be raised to about 80 to about 90 degrees Celsiusin the humidifier.

In alternative embodiments of the invention, the blower or compressor109 may provide the hydrogen rich stream into the humidifier 119 ratherthan into the fuel inlet conduit 111. If desired, the water drain 117may be used to provide additional water into the humidifier 119 by usinga pump or another water directing device. Furthermore, water from anexternal source and/or a humidified air exhaust stream from the stack101 may also be provided into the humidifier 119.

The system 100 also contains a recuperative heat exchanger 121 whichexchanges heat between the stack fuel exhaust stream and the hydrocarbonfuel inlet stream being provided from the humidifier 119. The heatexchanger helps to raise the temperature of the fuel inlet stream andreduces the temperature of the fuel exhaust stream so that it may befurther cooled in the condenser and such that it does not damage thehumidifier.

If the fuel cells are external fuel reformation type cells, then thesystem 100 contains a fuel reformer 123. The reformer 123 reforms ahydrocarbon fuel inlet stream into hydrogen and carbon monoxidecontaining fuel stream which is then provided into the stack 101. Thereformer 123 may be heated radiatively, convectively and/or conductivelyby the heat generated in the fuel cell stack 101 and/or by the heatgenerated in an optional burner/combustor, as described in U.S. patentapplication Ser. No. 11/002,681, filed Dec. 2, 2004, incorporated hereinby reference in its entirety. Alternatively, the external reformer 123may be omitted if the stack 101 contains cells of the internal reformingtype where reformation occurs primarily within the fuel cells of thestack.

Optionally, the system 100 also contains an air preheater heat exchanger125. This heat exchanger 125 heats the air inlet stream being providedto the fuel cell stack 101 using the heat of the fuel cell stack fuelexhaust. If desired, this heat exchanger 125 may be omitted.

The system 100 also preferably contains an air heat exchanger 127. Thisheat exchanger 127 further heats the air inlet stream being provided tothe fuel cell stack 101 using the heat of the fuel cell stack air (i.e.,oxidizer or cathode) exhaust. If the preheater heat exchanger 125 isomitted, then the air inlet stream is provided directly into the heatexchanger 127 by a blower or other air intake device.

The system may also contain an optional water-gas shift reactor 128. Thewater-gas shift reactor 128 may be any suitable device which converts atleast a portion of the water in the fuel exhaust stream into freehydrogen. For example, the reactor 128 may comprise a tube or conduitcontaining a catalyst which converts some or all of the carbon monoxideand water vapor in the fuel exhaust stream into carbon dioxide andhydrogen. Thus, the reactor 128 increases the amount of hydrogen in thefuel exhaust stream. The catalyst may be any suitable catalyst, such asa iron oxide or a chromium promoted iron oxide catalyst. The reactor 128may be located between the fuel heat exchanger 121 and the air preheaterheat exchanger 125. The water-gas shift reactor 128 may be used in asystem where the per pass fuel utilization in the stack is relativelylow, such as about 55 to 65% to maximize the amount of hydrogen providedto the hydrogen using device or storage vessel, or where the system isoperated to mainly generate electricity without generating a significantamount of hydrogen for the hydrogen using device or storage vessel.

The system 100 is operatively connected to a hydrogen storage vessel 129or a hydrogen using device 131. The hydrogen storage vessel may comprisea hydrogen storage tank or a hydrogen dispenser. The vessel may containa conduit leading to a hydrogen using device which is used intransportation, power generation, cooling, hydrogenation reactions, orsemiconductor manufacture. For example, the system 100 may be located ina chemical or a semiconductor plant to provide primary or secondary(i.e., backup) power for the plant as well as hydrogen for use inhydrogenation (i.e., passivation of semiconductor device) or otherchemical reactions which require hydrogen that are carried out in theplant.

The hydrogen using device 131 may also comprise another fuel cell system(such as a fuel cell stack), such as low temperature fuel cell system,such as a proton exchange membrane (PEM) fuel cell system, which useshydrogen as a fuel. Thus, the hydrogen from the system 100 is providedas fuel to one or more additional fuel cells 131. For example, thesystem 100 may be located in a stationary location, such as a buildingor an area outside or below a building and is used to provide power tothe building. The additional fuel cells 131 may be located in vehicleslocated in a garage or a parking area adjacent to the stationarylocation. A vehicle may comprise a car, sport utility vehicle, truck,motorcycle, boat or any other suitable fuel cell powered vehicle. Inthis case, the hydrocarbon fuel is provided to the system 100 togenerate electricity for the building and to generate hydrogen which isprovided as fuel to the fuel cell system 131 powered vehicles. Thegenerated hydrogen may be stored temporarily in the hydrogen storagevessel 129 and then provided from the storage vessel to the vehicle fuelcells 131 on demand (analogous to a gas station) or the generatedhydrogen may be provided directly from the system 100 to the vehiclefuel cells 131 through a conduit.

The system 100 may contain an optional hydrogen conditioner. Thehydrogen conditioner may be any suitable device which can purify, dry,compress (i.e., a compressor), or otherwise change the state point ofthe hydrogen-rich gas stream provided from the PPSA unit 1. If desired,the hydrogen conditioner may be omitted.

The hydrogen using device 131 may comprise a PEM fuel cell system oranother similar device which is generally carbon monoxide intolerant.Thus, carbon monoxide has to be scrubbed (i.e., removed by gasseparation and/or chemical reaction) from the hydrogen rich stream beingprovided from the PPSA unit 1 before the hydrogen rich stream isprovided into the PEM fuel cells located in a vehicle or into another COintolerant device 131.

In this case, the system 100 contains an optional carbon monoxidescrubbing device 133. The device 133 contains an inlet operativelyconnected to an outlet of the partial pressure swing adsorption unit 1and an outlet operatively connected to a PEM fuel cell system 131located in a vehicle. In operation, the carbon monoxide scrubbing device133 scrubs carbon monoxide being provided with the hydrogen from thepartial pressure swing adsorption unit 1 and provides the hydrogeneither directly or indirectly to the PEM fuel cell system 131.

The carbon monoxide scrubbing device 133 may comprise any device whichremoves carbon monoxide from the hydrogen rich stream by adsorption,chemical reaction and/or any other suitable method. The device 133 maycomprise a pressure swing adsorption unit and/or a Sabatier reactor. Forexample, as shown in FIG. 5, the scrubbing device comprises a Sabatierreactor 135 and a carbon monoxide polisher 137. The Sabatier reactorcomprises a tube or another container which contains a catalyst, such asa platinum family metal on an alumina support. Preferably, the catalystcomprises ruthenium. A gas mixture consisting primarily of hydrogen andcarbon monoxide is introduced into reactor tube from the PPSA system 1and contacts the catalyst therein. The gas mixture undergoes animmediate exothermic reaction and converts the carbon monoxide and someof the hydrogen to methane and water vapor. Remaining carbon monoxide isthen additionally scrubbed from the hydrogen, methane and water vaporgas stream in the polisher 137, which may comprise a silver basedadsorption device which adsorbs carbon monoxide. The polisher maycomprise plural adsorption beds where one bed adsorbs carbon monoxidewhile other beds are being regenerated. The outlet stream containinghydrogen, methane and water vapor from the polisher is then provided tothe hydrogen storage vessel 129 or the hydrogen using device 131 (theseparate purge gas outlet from the polisher 137 is not shown forclarity). The hydrogen may be used as the fuel in the PEM fuel cellsystem 131, the water vapor may be used to humidify the PEM electrolyteand the methane simply acts as a diluting gas in a PEM system.

Alternatively, the carbon monoxide scrubbing device 133 may comprise apressure swing adsorption (“PSA”) unit. This unit is similar to the PPSAunit 1, except that a reciprocating compressor is used to pressurize thefeed gas into one or more adsorbent beds which contain a material whichselectively adsorbs carbon monoxide compared to hydrogen. The pressureswing adsorption unit may operate on a Skarstrom-like PSA cycle. Theclassic Skarstrom cycle consists of four basic steps: pressurization,feed, blowdown, and purge. For example, the PSA unit may contain twoadsorbent beds. When one bed is undergoing pressurization and feed bythe compressor, the other column is undergoing blowdown and purge.Three-way valves may be used to direct the feed, purge and product gasesbetween the beds.

Alternatively, the device 131 may comprise a carbon monoxide tolerantelectrochemical cell, such as a stack of high-temperature, low-hydrationion exchange membrane cells. This type of cell includes anon-fluorinated ion exchange ionomer membrane, such as, for example, apolybenzimidazole (PBI) membrane, located between anode and cathodeelectrodes. The membrane is doped with an acid, such as sulfiric orphosphoric acid. An example of such cell is disclosed in US publishedapplication 2003/0196893, incorporated herein by reference in itsentirety. A stack 131 of these cells may be operated in a fuel cell modeto generate electricity for a vehicle or other uses when hydrogen isprovided to the cells of the stack. These cells are carbon monoxidetolerant and operate in a temperature range of above 100 to about 200degrees Celsius. Thus, the hydrogen containing stream is preferablyprovided to the stack 131 at a temperature above about 120 degreesCelsius. If a carbon monoxide tolerant device 131 is used, then thecarbon monoxide scrubbing device 133 is preferably omitted.

The system 100 of the fifth embodiment operates as follows. A fuel inletstream is provided into the fuel cell stack 101 through fuel inletconduit 111. The fuel may comprise any suitable fuel, such as ahydrocarbon fuel, including but not limited to methane, natural gaswhich contains methane with hydrogen and other gases, propane or otherbiogas, or a mixture of a carbon fuel, such as carbon monoxide,oxygenated carbon containing gas, such as methanol, or other carboncontaining gas with a hydrogen containing gas, such as water vapor, H₂gas or their mixtures. For example, the mixture may comprise syngasderived from coal or natural gas reformation.

The fuel inlet stream passes through the humidifier 119 where humidityis added to the fuel inlet stream. The humidified fuel inlet stream thenpasses through the fuel heat exchanger 121 where the humidified fuelinlet stream is heated by the fuel cell stack fuel exhaust stream. Theheated and humidified fuel inlet stream is then provided into a reformer123, which is preferably an external reformer. For example, reformer 123may comprise a reformer described in U.S. patent application Ser. No.11/002,681, filed on Dec. 2, 2004, incorporated herein by reference inits entirety. The fuel reformer 123 may be any suitable device which iscapable of partially or wholly reforming a hydrocarbon fuel to form acarbon containing and free hydrogen containing fuel. For example, thefuel reformer 123 may be any suitable device which can reform ahydrocarbon gas into a gas mixture of free hydrogen and a carboncontaining gas. For example, the fuel reformer 123 may comprise acatalyst coated passage where a humidified biogas, such as natural gas,is reformed via a steam-methane reformation reaction to form freehydrogen, carbon monoxide, carbon dioxide, water vapor and optionally aresidual amount of unreformed biogas. The free hydrogen and carbonmonoxide are then provided into the fuel (i.e., anode) inlet 105 of thefuel cell stack 101. Thus, with respect to the fuel inlet stream, thehumidifier 119 is located upstream of the heat exchanger 121 which islocated upstream of the reformer 123 which is located upstream of thestack 101.

The air or other oxygen containing gas (i.e., oxidizer) inlet stream ispreferably provided into the stack 101 through a heat exchanger 127,where it is heated by the air (i.e., cathode) exhaust stream from thefuel cell stack. If desired, the air inlet stream may also pass throughthe condenser 113 and/or the air preheat heat exchanger 125 to furtherincrease the temperature of the air before providing the air into thestack 101.

Once the fuel and air are provided into the fuel cell stack 101, thestack 101 is operated to generate electricity and a hydrogen containingfuel exhaust stream. The fuel exhaust stream (i.e., the stack anodeexhaust stream) is provided from the stack fuel exhaust outlet 103 intothe partial pressure swing adsorption unit 1. At least a portion ofhydrogen contained in the fuel exhaust stream is separated in the unit 1using a partial pressure swing adsorption. The hydrogen separated fromthe fuel exhaust stream in the unit 1 is then provided into the hydrogenstorage vessel 129 or the hydrogen using device 131. Optionally, aportion of the separated hydrogen is also provided back into the fuelinlet stream in fuel inlet conduit 111 upstream of the humidifier 119.

The fuel exhaust stream is provided into the unit 1 as follows. The fuelexhaust stream may contain hydrogen, water vapor, carbon monoxide,carbon dioxide, some unreacted hydrocarbon gas, such as methane andother reaction by-products and impurities. For example, the fuel exhaustmay have a flow rate of between 160 and 225 slpm, such as about 186 toabout 196 slpm, and may comprise between about 45 to about 55%, such asabout 48-50% hydrogen, about 40 to about 50%, such as about 45-47%carbon dioxide, about 2% to about 4%, such as about 3% water and about1% to about 2% carbon monoxide.

This exhaust stream is first provided into the heat exchanger 121, whereits temperature is lowered, preferably to less than 200 degrees Celsius,while the temperature of the fuel inlet stream is raised. If the airpreheater heat exchanger 125 is present, then the fuel exhaust stream isprovided through this heat exchanger 125 to further lower itstemperature while raising the temperature of the air inlet stream. Thetemperature may be lowered to 90 to 110 degrees Celsius for example.

The fuel exhaust stream is then provided into the fuel humidifier 119where a portion of the water vapor in the fuel exhaust stream istransferred to the fuel inlet stream to humidify the fuel inlet stream.The fuel exhaust stream is then provided into the condenser 113 where itis further cooled to condense additional water vapor from the fuelexhaust stream. The fuel exhaust stream may be cooled in the condenserby the fuel cell stack air inlet stream or by a different air inletstream or by another cooling fluid stream. The water condensed from thefuel exhaust stream is collected in the liquid state in the waterseparator 115. Water may be discharged from the separator 115 viaconduit 117 and then drained away or reused.

The remaining fuel exhaust stream gas is then provided from theseparator 115 as the feed gas inlet stream into inlet 2 of the partialpressure swing adsorption unit 1 via conduit 3. Furthermore, the purgegas inlet stream, such as a dried air stream is provided into the unit 1from blower or compressor 6 through conduit 5 into inlet 4. If desired,the air stream may be dried using additional adsorbent beds in atemperature swing adsorption cycle before being provided into adsorbentbeds 11, 13 of the unit 1. In this case, the heated air used in thetemperature swing adsorption cycle to dry the silica gel or alumina inthe adsorbent beds may be removed from unit 1 via a vent conduit 139.

Thus, the fuel exhaust stream comprises hydrogen, carbon monoxide, watervapor, carbon dioxide as well as possible impurities and unreactedhydrocarbon fuel. During the separation step in unit 1, at least amajority of the water vapor and carbon dioxide in the fuel exhauststream are adsorbed in at least one adsorbent bed 11, 13 while allowingat least a majority of the hydrogen and carbon monoxide in the fuelexhaust stream to be passed through the at least one adsorbent bed.Specifically, unpressurized fuel exhaust stream is provided into thefirst adsorbent bed 11 to adsorb at least a majority of the water vaporand carbon dioxide remaining in the fuel exhaust stream in the firstadsorbent bed until the first adsorbent bed is saturated, while thesecond adsorbent bed 13 is regenerated by providing air having arelative humidity of 50% or less at about 30 degrees Celsius through thesecond adsorbent bed to desorb adsorbed carbon dioxide and water vapor.After the first bed 11 is saturated with carbon dioxide, theunpressurized fuel exhaust stream is provided into the second adsorbentbed 13 to adsorb at least a majority of the remaining water vapor andcarbon dioxide in the fuel exhaust stream in the second adsorbent beduntil the second adsorbent bed is saturated while regenerating the firstadsorbent bed by providing air having a relative humidity of 50% or lessat about 30 degrees Celsius through the first adsorbent bed 11 to desorbthe adsorbed carbon dioxide and water vapor.

The hydrogen and carbon monoxide separated from the fuel exhaust stream(i.e., feed gas outlet stream) are then removed from unit 1 throughoutlet 8 and conduit 7 and provided into the selector valve 108. Thevalve 108 divides the hydrogen containing stream provided from the PPSAunit 1 into a first stream, which is provided into the hydrocarbon fuelinlet stream in the inlet conduit 111, and a second stream which isprovided to the hydrogen storage vessel 129 or the hydrogen using device131.

The valve 108 may divide the hydrogen containing stream intocontemporaneous first and second streams, such that the first and thesecond streams are provided from the valve 108 at the same time. Thevalve 108 may vary the ratio of how much of the hydrogen containingstream provided from the PPSA unit 1 is provided into a first stream andhow much of the hydrogen containing stream is provided into the secondstream over time. Alternatively, the valve 108 may alternate betweenproviding at least 90-100% of the hydrogen containing stream into thehydrocarbon fuel inlet stream and providing 90 to 100% of the hydrogencontaining stream to the hydrogen storage vessel 129, for example. Ifdesired one of the steams may be omitted and the valve 108 may simplyconstantly direct the hydrogen containing stream into either the vessel129/device 131 or into the fuel inlet conduit 111.

The valve 108 may be operated by a computer and/or by an operator tocontrollably provide a desired amount of hydrogen into the fuel inletstream and/or to one of the hydrogen storage vessel and the hydrogenusing device. The computer or operator may vary this amount based on anysuitable parameter. The parameters include: i) detected or observedconditions of the system 100 (i.e., changes in the system operatingconditions requiring a change in the amount of hydrogen or CO in thefuel inlet stream); ii) previous calculations provided into the computeror conditions known to the operator which require a temporal adjustmentof the hydrogen or CO in the fuel inlet stream; iii) desired futurechanges, presently occurring changes or recent past changes in theoperating parameters of the stack 101, such as changes in theelectricity demand by the users of electricity generated by the stack,changes in price for electricity or hydrocarbon fuel compared to theprice of hydrogen, etc., and/or iv) changes in the demand for hydrogenby the hydrogen user, such as the hydrogen using device, changes inprice of hydrogen or hydrocarbon fuel compared to the price ofelectricity, etc.

The second hydrogen rich stream may be provided directly to vessel 129or device 131 or it may first be provided through the carbon monoxidescrubbing device 133 to scrub carbon monoxide from the second streambefore providing the stream to a carbon monoxide intolerant device. Forexample, the second hydrogen stream may be first provided to thehydrogen storage vessel 129 and then provided from the hydrogen storagevessel 129 to the hydrogen using device, such as a PEM fuel cell system131 in a vehicle, on demand or according to a predefined schedule.Alternatively, the second hydrogen stream may be provided to thehydrogen using device, such as a PEM fuel cell system 131 without firstbeing provided to the hydrogen storage vessel 129.

The first hydrogen rich stream provided from the selector valve isrecycled into the fuel inlet stream in the fuel inlet conduit 111.Preferably, this first hydrogen rich stream containing hydrogen andcarbon monoxide is first provided into a blower or compressor 109, whichis then used to controllably provide a desired amount of hydrogen andcarbon monoxide separated from the fuel exhaust stream into the fuelinlet stream. The blower or compressor 109 may be operated by a computeror by an operator to controllably provide a desired amount of hydrogenand carbon monoxide into the fuel inlet stream, and may vary this amountbased on any suitable parameter. The parameters include: i) detected orobserved conditions of the system 100 (i.e., changes in the systemoperating conditions requiring a change in the amount of hydrogen or COin the fuel inlet stream); ii) previous calculations provided into thecomputer or conditions known to the operator which require a temporaladjustment of the hydrogen or CO in the fuel inlet stream; and/or iii)desired future changes, presently occurring changes or recent pastchanges in the operating parameters of the stack 101, such as changes inthe electricity demand by the users of electricity generated by thestack, etc. Thus, the blower or compressor may controllably vary theamount of hydrogen and carbon monoxide provided into the fuel inletstream based on the above described and/or other criteria. Since thehydrogen and carbon monoxide are cooled to 200 degrees Celsius or less,a low temperature blower may be used to controllably provide thehydrogen and carbon monoxide into the conduit 111. If desired, theselector valve 108 and the blower or compressor 109 may be omitted andthe entire hydrogen rich stream may be provided from the PPSA unit 1 tothe hydrogen storage vessel 129 or the hydrogen using device 131.

The purge gas outlet stream from the PPSA unit may contain a traceamount of hydrogen and/or hydrocarbon gases trapped in the void volumesof the adsorbent beds. In other words, some trapped hydrogen orhydrocarbon gas may not be removed into conduit 7 by the flush steps.Thus, it is preferred that conduit 9 provide the purge gas outlet streamfrom PPSA unit 1 to a burner 107. The stack 101 air exhaust stream isalso provided through heat exchanger 127 into the burner 107. Anyremaining hydrogen or hydrocarbon gas in the purge gas outlet stream isthen burned in the burner to avoid polluting the environment. The heatfrom the burner 107 may be used to heat the reformer 123 or it may beprovided to other parts of the system 100 or to a heat consuming devicesoutside the system 100, such as a building heating system.

Thus, with respect to the fuel exhaust stream, the heat exchanger 121 islocated upstream of the heat exchanger 125, which is located upstream ofthe humidifier 119, which is located upstream of the condenser 113 andwater separator 115, which is located upstream of the PPSA unit 1, whichis located upstream of blower or compressor 109 which is locatedupstream of the fuel inlet conduit 111.

FIG. 6 illustrates a system 200 according to the sixth embodiment of theinvention. The system 200 is similar to system 100 and contains a numberof components in common. Those components which are common to bothsystems 100 and 200 are numbered with the same numbers in FIGS. 5 and 6and will not be described further.

One difference between systems 100 and 200 is that system 200preferably, but not necessarily lacks, the humidifier 119. Instead, aportion of the water vapor containing stack fuel exhaust stream isdirectly recycled into the stack fuel inlet stream. The water vapor inthe fuel exhaust stream is sufficient to humidify the fuel inlet stream.

The system 200 contains a fuel splitter device 201, such as a computeror operator controlled multi-way valve, for example a three-way valve,or another fluid splitting device. The device 201 contains an inlet 203operatively connected to the fuel cell stack fuel exhaust outlet 103, afirst outlet 205 operatively connected to the condenser 113 and waterseparator 115 and a second outlet 207 operatively connected to the fuelcell stack fuel inlet 105. For example, the second outlet 207 may beoperatively connected to the fuel inlet conduit 111, which isoperatively connected to inlet 105. However, the second outlet 207 mayprovide a portion of the fuel exhaust stream into the fuel inlet streamfurther downstream.

Preferably, the system 200 contains a second blower or compressor 209which provides the fuel exhaust stream into the fuel inlet stream.Specifically, the outlet 207 of the valve 201 is operatively connectedto an inlet of the blower or compressor 209, while an outlet of theblower or compressor 209 is connected to the hydrocarbon fuel inletconduit 111. In operation, the blower or compressor 209 controllablyprovides a desired amount of the fuel cell stack fuel exhaust streaminto the fuel cell stack fuel inlet stream.

The method of operating the system 200 is similar to the method ofoperating the system 100. One difference is that the fuel exhaust streamis separated into at least two streams by the device 201. The first fuelexhaust stream is recycled into the fuel inlet stream, while the secondstream is directed into the PPSA unit 1 where at least a portion ofhydrogen contained in the second fuel exhaust stream is separated usingthe partial pressure swing adsorption. At least a portion of thehydrogen separated from the second fuel exhaust stream is then providedinto the hydrogen storage vessel 129 or the hydrogen using device 131,and optionally a portion of the hydrogen and carbon monoxide separatedfrom the second fuel exhaust stream are provided into the fuel inletstream in the fuel inlet conduit 111. For example, between 50 and 70%,such as about 60% of the fuel exhaust stream may be provided to thesecond blower or compressor 209, while the remainder may be providedtoward the PPSA unit 1.

Preferably, the fuel exhaust stream is first provided through the heatexchangers 121 and 125 before being provided into the valve 201. Thefuel exhaust stream is cooled to 200 degrees Celsius or less, such as to90 to 180 degrees, in the heat exchanger 125 prior to being providedinto the valve 201 where it is separated into two streams. This allowsthe use of a low temperature blower 209 to controllably recycle adesired amount of the first fuel exhaust stream into the fuel inletstream, since such blower may be adapted to move a gas stream which hasa temperature of 200 degrees Celsius or less.

The second blower or compressor 209 may be computer or operatorcontrolled and may vary the amount of the fuel exhaust stream beingprovided into the fuel inlet stream depending on the conditionsdescribed above with respect to the fifth embodiment. Furthermore, thesecond blower or compressor may be operated in tandem with the firstblower or compressor 109. Thus, the operator or computer may separatelyvary the amount of hydrogen being provided into vessel 129 or device131, the amount of hydrogen and carbon monoxide being provided into thefuel inlet stream by the first blower or compressor 109, and the amountof fuel exhaust stream being provided into the fuel inlet stream by thesecond blower or compressor 209 based on any suitable criteria, such asthe criteria described above with respect to the fifth embodiment.Furthermore, the computer or operator may take into account both theamount of hydrogen and carbon monoxide being provided into the fuelinlet stream by the first blower or compressor 109 and the amount offuel exhaust stream being provided into the fuel inlet stream by thesecond blower or compressor 209 and optimize the amount of both based onthe criteria described above.

If desired, the features of the fifth and sixth embodiments may becombined. For example, the three way valve 201 and the fuel exhauststream recycling from FIG. 6 may be used together with the humidifier119 from FIG. 5 in a single system. Such a system could then be operatedin different modes to optimize electricity generation or to optimizehydrogen production for the hydrogen storage vessel 129 or the hydrogenusing device 131. The system may be switched between different modesdepending on the demand for and/or price of electricity and hydrogen orother factors.

When the system is operated to optimize electricity generation (i.e., tooptimize the AC electrical efficiency of the system), the selector valve108 provides the entire hydrogen rich stream from the PPSA unit 1 backinto the fuel inlet conduit. The valve 201 provides a portion of thefuel exhaust stream into the fuel inlet conduit 111 to humidify the fuelinlet stream. In this case, the valve 201 may route the fuel exhauststream into the fuel inlet conduit to by-pass the humidifier 119. Theper pass fuel utilization rate is maximized to the highest reasonableoperating value, such as about 75% to about 80%, for example, tooptimize the electricity production. In this case, no hydrogen isprovided to the hydrogen storage vessel 129 or to the hydrogen usingdevice 131.

When the system is operated to optimize hydrogen generation for thehydrogen storage vessel 129 or to the hydrogen using device 131, theselector valve 108 provides the entire hydrogen rich stream from thePPSA unit 1 to the hydrogen storage vessel 129 or to the hydrogen usingdevice 131. No hydrogen rich stream is provided into the fuel inletconduit. In this case, the valve 201 provides the entire fuel exhauststream from the stack into the humidifier 119 where the fuel inletstream is humidified, rather than providing a portion of the fuelexhaust stream into the fuel inlet conduit 111. The per pass fuelutilization rate is minimized to the lowest reasonable operating value,such as about 55% to about 60%, for example, to optimize the hydrogenproduction. In this case, a maximum amount of hydrogen is provided tothe hydrogen storage vessel 129 or to the hydrogen using device 131.Furthermore, more hydrocarbon fuel may be provided to the fuel cellstack when the system operates to optimize hydrogen production than whenthe system operates to optimize electrical efficiency. For example,50-100% more hydrocarbon fuel is provided to the stack 101 when thesystem is operating to optimize hydrogen production than when the systemis operating to optimize electrical efficiency.

The system may also be operated to balance electrical efficiency andhydrogen production. In this case, the selector valve 108 splits thehydrogen rich stream from the PPSA unit 1 between the fuel inlet conduit111 and the hydrogen storage vessel 129/hydrogen using device 131. Bothsteams may be provided at the same time or the valve may alternatebetween providing the first and the second streams. The amount ofhydrogen provided between the two streams can be varied depending on theconditions described above. In this case, the valve 201 may provide thefuel exhaust stream into the fuel inlet stream and/or into thehumidifier 119, depending on the desired parameters.

Table I below illustrates several exemplary operating modes for thesystem to generate the same power output of 26.8 kW. The first mode isthe electrical efficiency optimization mode described above, where theselector valve 108 provides the entire hydrogen rich stream into thefuel inlet conduit 111 (“hydrogen recycle ON”) and valve 201 provides aportion of the fuel exhaust stream into the fuel inlet conduit 111(“fuel exhaust recycle ON”). The electrical efficiency is optimized toabout 58% for a relatively low natural gas fuel flow rate. The secondmode is similar to the first mode, except that valve 201 provides thefuel exhaust stream to the humidifier 119 which humidifies the fuelinlet stream (the hydrogen recycle is ON while the fuel exhaust recycleis OFF).

The third mode is the opposite of the second mode, where the selectorvalve 108 provides the hydrogen rich stream into the vessel 129/device131 (“hydrogen recycle OFF”) and the valve 201 provides a portion of thefuel exhaust stream into the fuel inlet conduit 111 (“fuel exhaustrecycle ON”).

The fourth and fifth modes are the hydrogen generation optimizationmodes, where the selector valve 108 provides the hydrogen rich stream tovessel 129 or device 131 (“hydrogen recycle OFF”) and the humidifier 119is used to humidify the fuel inlet stream (“fuel exhaust recycle OFF”).In the fifth mode, the per pass fuel utilization rate is decreased 20%and the natural gas flow rate is increased compared to the fourth modeto more than triple the hydrogen generation. Thus, in the fifth mode,the hydrogen generation is optimized at the expense of the lowelectrical efficiency (below 40%), low per pass fuel utilization rate(55%) and a relatively high natural gas fuel flow rate.

TABLE I Recycle Hydrogen Streams Fuel Natural gas Electrical generated,Mode ON/OFF utilization, % MMBtu/hr efficiency, % kg/day 1 Fuel Exhaust75 0.16 57.9 0 Recycle ON + Hydrogen Recycle ON 2 Fuel Exhaust 75 0.1851.5 0 Recycle OFF + Hydrogen Recycle ON 3 Fuel Exhaust 75 0.17 55.4 1.4Recycle ON + Hydrogen Recycle OFF 4 Fuel Exhaust 75 0.20 46.3 5.4Recycle OFF + Hydrogen Recycle OFF 5 Fuel Exhaust 55 0.27 33.8 19.1Recycle OFF + Hydrogen Recycle OFF

The fuel cell systems described herein may have other embodiments andconfigurations, as desired. Other components may be added if desired, asdescribed, for example, in U.S. application Ser. No. 10/300,021, filedon Nov. 20, 2002, in U.S. Provisional Application Ser. No. 60/461,190,filed on Apr. 9, 2003, and in U.S. application Ser. No. 10/446,704,filed on May 29, 2003 all incorporated herein by reference in theirentirety. Furthermore, it should be understood that any system elementor method step described in any embodiment and/or illustrated in anyfigure herein may also be used in systems and/or methods of othersuitable embodiments described above, even if such use is not expresslydescribed.

The foregoing description of the invention has been presented forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed, andmodifications and variations are possible in light of the aboveteachings or may be acquired from practice of the invention. Thedescription was chosen in order to explain the principles of theinvention and its practical application. It is intended that the scopeof the invention be defined by the claims appended hereto, and theirequivalents.

1. A method of operating a fuel cell system, comprising: providing afuel inlet stream into a fuel cell stack; operating the fuel cell stackto generate electricity and a hydrogen containing fuel exhaust stream;separating at least a portion of hydrogen contained in the fuel exhauststream using partial pressure swing adsorption; and providing thehydrogen separated from the fuel exhaust stream to a hydrogen storagevessel or to a hydrogen using device; wherein the step of separatingcomprises: (a) a first feed/purge step comprising: providing a feed gasinlet stream comprising at least a portion of the fuel exhaust streaminto a first adsorbent bed; collecting a feed gas outlet streamcomprising at least one separated component of the feed gas at a firstoutput; providing a purge gas inlet stream into a second adsorbent bed;and collecting a purge gas outlet stream at a second output; (b) a firstflush step, conducted after the first feed/purge step, the first flushstep comprising: providing the purge gas inlet stream into the firstadsorbent bed; collecting the purge gas outlet stream, which comprisesat least one component of the feed gas that was trapped in a void volumeof the first adsorbent bed, at the first output; providing the feed gasinlet stream into the second adsorbent bed; and collecting the feed gasoutlet stream, which comprises a portion of the purge gas that wastrapped in a void volume of the second bed, at the second output; (c) asecond feed/purge step, conducted after the first flush step, the secondfeed/purge step comprising: providing the feed gas inlet stream into thesecond adsorbent bed; collecting the feed gas outlet stream comprisingat least one separated component of the feed gas at the first output;providing the purge gas inlet stream into the first adsorbent bed; andcollecting the purge gas outlet stream at the second output; and (d) asecond flush step, conducted after the second feed/purge step, thesecond flush step comprising: providing the purge gas inlet stream intothe second adsorbent bed; collecting the purge gas outlet stream, whichcomprises at least one component of the feed gas that was trapped in avoid volume of the second adsorbent bed, at the first output; providingthe feed gas inlet stream into the first adsorbent bed; and collecting afeed gas outlet stream, which comprises a portion of the purge gas thatwas trapped in a void volume of the first bed, at the second output. 2.The method of claim 1, wherein: the fuel inlet stream comprises ahydrocarbon fuel inlet stream; the fuel cell stack comprises a solidoxide fuel cell stack; the fuel exhaust stream comprises hydrogen,carbon monoxide, water vapor and carbon dioxide; and the step ofseparating comprises adsorbing at least a majority of the carbon dioxideand a portion of the water vapor in the fuel exhaust stream in at leastone adsorbent bed while allowing at least a majority of the hydrogen andcarbon monoxide in the fuel exhaust stream to be passed through the atleast one adsorbent bed.
 3. The method of claim 2, the step ofseparating comprises: providing unpressurized fuel exhaust stream into afirst adsorbent bed to adsorb at least a majority of the carbon dioxideand a portion of the water vapor in the fuel exhaust stream in the firstadsorbent bed until the first adsorbent bed is saturated whileregenerating a second adsorbent bed by providing air having a relativehumidity of 50% or less through the second adsorbent bed to desorbadsorbed carbon dioxide and water vapor; and providing unpressurizedfuel exhaust stream into the second adsorbent bed to adsorb at least amajority of the carbon dioxide and a portion of the water vapor in thefuel exhaust stream in the second adsorbent bed until the secondadsorbent bed is saturated while regenerating the first adsorbent bed byproviding air having a relative humidity of 50% or less through thefirst adsorbent bed to desorb adsorbed carbon dioxide and water vapor.4. The method of claim 2, wherein the step of providing the hydrogencomprises providing the hydrogen separated from the fuel exhaust streamto the hydrogen storage vessel.
 5. The method of claim 2, wherein thestep of providing the hydrogen comprises providing the hydrogenseparated from the fuel exhaust stream to the hydrogen using device. 6.The method of claim 2, wherein: the hydrogen using device comprises aPEM fuel cell system located in a vehicle; and the step of providing thehydrogen comprises providing the hydrogen to the hydrogen storage vesseland then providing the hydrogen from the hydrogen storage vessel to thePEM fuel cell system, or providing the hydrogen to the PEM fuel cellsystem without providing the hydrogen to the hydrogen storage vessel. 7.The method of claim 6, further comprising scrubbing carbon monoxide froma hydrogen containing stream before the step of providing hydrogen tothe PEM fuel cell system and after the step of separating the hydrogenfrom the fuel exhaust stream by partial pressure swing adsorption. 8.The method of claim 7, wherein the step of scrubbing carbon monoxidecomprises scrubbing carbon monoxide using pressure swing adsorption or aSabatier reaction.
 9. The method of claim 2, further comprising:dividing the hydrogen separated from the fuel exhaust stream into afirst stream and a second stream; providing the first stream into thehydrocarbon fuel inlet stream; and providing the second stream to thehydrogen storage vessel or the hydrogen using device.
 10. The method ofclaim 9, further comprising alternating between providing the hydrogenseparated from the fuel exhaust stream into the hydrocarbon fuel inletstream and providing the hydrogen separated from the fuel exhaust to thehydrogen storage vessel.
 11. The method of claim 1, further comprising:humidifying the fuel inlet stream using water vapor contained in thefuel exhaust stream by using a humidifier; after the step ofhumidifying, condensing and removing at least a part of the water vaporin the fuel exhaust stream; performing the step of separating after thestep of condensing and removing; and providing all hydrogen separatedfrom the fuel exhaust stream to a hydrogen storage vessel or to ahydrogen using device without recycling hydrogen separated from the fuelexhaust stream into the fuel inlet stream and without recycling aportion of the fuel exhaust stream into the fuel inlet stream.
 12. Themethod of claim 1, further comprising: separating the fuel exhauststream into at least two streams; recycling a first fuel exhaust streaminto the fuel inlet stream; separating at least a portion of hydrogenand carbon monoxide contained in a second fuel exhaust stream using thepartial pressure swing adsorption; providing a first portion of theseparated hydrogen to the hydrogen using device or to the hydrogenstorage vessel; and providing a second portion of the separated hydrogento the fuel inlet stream.
 13. A fuel cell system, comprising: a fuelcell stack; a partial pressure swing adsorption unit comprising aplurality of adsorbent beds; a first conduit which operatively connectsa fuel exhaust outlet of the fuel cell stack to a first inlet of thepartial pressure swing adsorption unit; a second conduit whichoperatively connects a purge gas source to a second inlet of the partialpressure swing adsorption unit; and a third conduit which operativelyconnects an outlet of the partial pressure swing adsorption unit to ahydrogen using device or to a hydrogen storage vessel; the plurality ofadsorbent beds comprise a first adsorbent bed and a second adsorbentbed; in operation, the first adsorbent bed performs the followingfunctions: (a) receives the feed gas inlet stream comprising at least aportion of the fuel cell stack fuel exhaust stream from the firstconduit and provides at least one separated component of the feed gas tothe third conduit in a first feed/purge step; (b) receives the purge gasinlet stream from the second conduit and provides a purge gas outletstream, which comprises at least one component of the feed gas that wastrapped in a void volume of the first bed to the third conduit in afirst flush step, conducted after the first feed/purge step; (c)receives a purge gas inlet stream from the second conduit and provides apurge gas outlet stream to an output different from the third conduit ina second feed/purge step, conducted after the first flush step; and (d)receives the feed gas inlet stream from the first conduit and provides afeed gas outlet stream, which comprises a portion of the purge gas thatwas trapped in a void volume of the first bed, to at an output differentfrom the third conduit in a second flush step, conducted after thesecond feed/purge step; and in operation, the second bed performs thefollowing functions: (a) receives a purge gas inlet stream from thesecond conduit and provides a purge gas outlet stream to at an outputdifferent from the third conduit in a first feed/purge step; (b)receives the feed gas inlet stream from the first conduit and providesthe feed gas outlet stream, which comprises a portion of the purge gasthat was trapped in a void volume of the second bed, to an outputdifferent from the third conduit in a first flush step, conducted afterthe first feed/purge step; (c) receives the feed gas inlet stream fromthe first conduit and provides the feed gas outlet stream comprising atleast one separated component of the feed gas to the third conduit in asecond feed/purge step, conducted after the first flush step; and (d)receives the purge gas inlet stream from the second conduit and providesthe purge gas outlet stream, which comprises at least one component ofthe feed gas that was trapped in a void volume of the second bed to thefirst conduit in a second flush step, conducted after the secondfeed/purge step.
 14. The system of claim 13, wherein: the fuel cellstack comprises a solid oxide fuel cell stack; the plurality ofadsorbent beds comprise a material which preferentially adsorbs carbondioxide and water vapor to hydrogen and carbon monoxide; and the systemlacks a compressor which in operation compresses the fuel cell stackfuel exhaust stream to be provided into the partial pressure swingadsorption unit.
 15. The system of claim 13, wherein the third conduitoperatively connects an outlet of the partial pressure swing adsorptionunit to the hydrogen storage vessel.
 16. The system of claim 13, whereinthe third conduit operatively connects an outlet of the partial pressureswing adsorption unit to the hydrogen using device.
 17. The system ofclaim 13, further comprising a selector valve having an inletoperatively connected to an outlet of the partial pressure swingadsorption unit, a first outlet operatively connected to the hydrogenstorage vessel or to the hydrogen using device, and a second outletoperatively connected to a fuel inlet of the fuel cell stack.
 18. Thesystem of claim 17, further comprising a carbon monoxide scrubbingdevice having an inlet operatively connected to an outlet of the partialpressure swing adsorption unit and an outlet operatively connected to aPEM fuel cell system located in a vehicle, wherein in operation, thecarbon monoxide scrubbing device scrubs carbon monoxide being providedwith the hydrogen from the partial pressure swing adsorption unit andprovides the hydrogen either directly or indirectly to the PEM fuel cellsystem.
 19. The system of claim 18, wherein the carbon monoxidescrubbing device comprises a pressure swing adsorption unit or aSabatier reactor.
 20. The system of claim 13, further comprising: acondenser and water separator having an inlet which is operativelyconnected to the fuel cell stack fuel exhaust outlet and an outlet whichis operatively connected to an inlet of the partial pressure swingadsorption unit; and a fuel humidifier having a first inlet operativelyconnected to a hydrocarbon fuel inlet conduit, a second inletoperatively connected to the fuel cell stack fuel exhaust outlet, afirst outlet operatively connected to the fuel cell stack fuel inlet,and a second outlet operatively connected to the condenser and waterseparator, wherein in operation, the fuel humidifier humidifies a fuelinlet stream using water vapor contained in a fuel cell stack fuelexhaust stream.
 21. The system of claim 13, further comprising: acondenser and water separator having an inlet which is operativelyconnected to the fuel cell stack fuel exhaust outlet and an outlet whichis operatively connected to an inlet of the partial pressure swingadsorption unit; and a multi-way valve having an inlet operativelyconnected to the fuel cell stack fuel exhaust outlet, a first outletoperatively connected to the condenser and water separator, and a secondoutlet operatively connected to the fuel cell stack fuel inlet conduit.22. A fuel cell system, comprising: a fuel cell stack; and a separationmeans for separating at least a portion of hydrogen contained in a fuelcell stack fuel exhaust stream using partial pressure swing adsorptionand for providing the hydrogen separated from the fuel exhaust stream toa hydrogen storage vessel or to a hydrogen using device; wherein theseparation means comprises: a first means for providing a feed gas inletstream comprising at least a portion of the fuel cell stack fuel exhauststream; a second means for providing a purge gas inlet stream; a thirdmeans for collecting at least one separated component of the feed gas; afourth means for: (a) receiving the feed gas inlet stream from the firstmeans and for providing at least one separated component of the feed gasto the third means in a first feed/purge step; (b) receiving the purgegas inlet stream from the second means and for providing a purge gasoutlet stream, which comprises at least one component of the feed gasthat was trapped in a void volume of the fourth means to the third meansin a first flush step, conducted after the first feed/purge step; (c)receiving a purge gas inlet stream from the second means and forproviding a purge gas outlet stream to an output different from thethird means in a second feed/purge step, conducted after the first flushstep; and (d) receiving the feed gas inlet stream from the first meansand for providing a feed gas outlet stream, which comprises a portion ofthe purge gas that was trapped in a void volume of the fourth means, toat an output different from the third means, in a second flush step,conducted after the second feed/purge step; a fifth means for: (a)receiving a purge gas inlet stream from the second means and forproviding a purge gas outlet stream to at an output different from thethird means in a first feed/purge step; (b) receiving the feed gas inletstream from the first means and for providing the feed gas outletstream, which comprises a portion of the purge gas that was trapped in avoid volume of the fifth means, to an output different from the thirdmeans in a first flush step, conducted after the first feed/purge step;(c) receiving the feed gas inlet stream from the first means and forproviding the feed gas outlet stream comprising at least one separatedcomponent of the feed gas to the third means in a second feed/purgestep, conducted after the first flush step; and (d) receiving the purgegas inlet stream from the second means and for providing the purge gasoutlet stream, which comprises at least one component of the feed gasthat was trapped in a void volume of the fifth means to the first meansin a second flush step, conducted after the second feed/purge step; anda sixth means for dividing the hydrogen separated from the fuel exhauststream into a first stream and a second stream, for providing the firststream into the hydrocarbon fuel inlet stream, and for providing thesecond stream to the hydrogen storage vessel or the hydrogen usingdevice.
 23. The system of claim 22, wherein the separation means is ameans for separating at least the portion of hydrogen contained in thefuel cell stack fuel exhaust stream using partial pressure swingadsorption and for providing the hydrogen separated from the fuelexhaust stream to a PEM fuel cell system located in a vehicle either byproviding the hydrogen to the hydrogen storage vessel, which thenprovides the hydrogen to the PEM fuel cell system, or by providing thehydrogen to the PEM fuel cell system without providing the hydrogen tothe hydrogen storage vessel.
 24. The system of claim 22, furthercomprising a scrubbing means for scrubbing carbon monoxide from a gasstream provided from the separation means to the hydrogen storage vesselor to the hydrogen using device.
 25. The system of claim 22, wherein:the fuel inlet stream comprises a hydrocarbon fuel inlet stream; thefuel cell stack comprises a solid oxide fuel cell stack; the fuelexhaust stream comprises hydrogen, carbon monoxide, water vapor andcarbon dioxide; and the separation means is a means for adsorbing atleast a majority of the carbon dioxide and a portion of the water vaporin the fuel exhaust stream while allowing at least a majority of thehydrogen and carbon monoxide in the fuel exhaust stream to be passedthrough.